Can't find remesh button
To the main question, remesh can be found in 2 places when in sculpt mode. One is in the header of the 3D View to the right, maybe you need to scroll it with the "alt+click" on your pen or middle mouse button, the second one is in the Active Tools and Workspace Settings, right above the Render Properties tab, there between Options and Workspace. 

Regarding the switching of objects while in sculpt mode, since you are using the middle mouse button emulation, the alt is not working since it's used for rotating the 3D View.
You may have to use "ctrl-tab" to open a pie menu and select "object-mode", to switch back, well same pie-menu. Sadly the one keymap that could make it easier is non-modal, means it would overwrite not only the mode change in sculpting, but also in the object-mode. If you primary use sculpting it may be interesting for you non the less. In the second picture, the marked "Edit Mode" can be changed to "Object Mode", but as i mentioned it will toggle not only in sculpt mode, but also in other modes. You can always reset it back to "Edit Mode" though. It seems that you may need to switch at least once manually back to sculpt mode if you add a new object after switching from sculpt mode and select the new object, from then on it usually works fine with just "tab" to change mode, change selection and "tab" back, happy sculpting.